Semiconductor photoimagers, which are also commonly referred to more simply as “photoimagers,” are used in a variety of different types of electronic devices, including digital cameras, wireless devices with picture capabilities (e.g., cell phones, so-called “personal digital assistants” (PDAs), etc.), IP security cameras, intelligent vehicle systems, and medical devices. The use of photoimagers has increased as they have been made smaller and capable of producing clearer images with higher pixel resolution.
Examples of photoimagers include the more conventional charge-coupled devices (CCDs), as well as state-of-the-art complementary metal-oxide-semiconductor (CMOS) imagers. CMOS imagers are becoming increasingly more popular because they offer several advantages over CCDs, including lower manufacturing costs, lower power consumption, ease of system design, smaller dimensions, and on-chip feature sets. Many of the desirable features of CMOS imagers may be attributed to the use of semiconductor device fabrication technology and equipment.
Conventionally, photoimagers have been wirebonded to carriers, or carrier substrates, such as circuit boards. As a relatively large portion of the active surface is dedicated to image sensing, all of the bond pads of a photoimager are confined to the periphery. As a consequence, the periphery of the photoimager may be densely populated with bond pads and their corresponding bond wires. Further, the bond wires consume valuable real estate on the carrier substrate.
Through-wafer interconnects (TWIs), or conductive vias, have been developed to alleviate many of the problems associated with the bond pads of conventional photoimagers and the bond wires that have been used to electrically connect conventionally configured photoimagers to carriers. By rerouting bond pads to the back side of a photoimager, through-wafer interconnects enable the placement of glass covers over photoimagers, eliminate the need for bond wires, reduce required real-estate, increase device density, and enable the use of wafer-level packaging methods. Conventional through-wafer interconnects, however, like wire bonding, require front-side processing, which may contaminate the image sensing elements of a photoimager.
The back side of the substrate upon which a photoimager is fabricated may be ground or etched to reduce the thickness of the photoimager and, thus, to reduce the volume of space consumed by the photoimager. Conventional grinding processes have been used to reduce the thicknesses of photoimagers to as low as about 100 μm. Photoimagers that are thinner than about 100 μm have not been possible, however, due to warpage, bowing, cracking, and breakage that occurs when back grinding processes are used to reduce wafer thicknesses below about 100 μm.
There are needs for processes and features to protect image sensing elements of a photoimager as the photoimager is subjected to processing from its back side.
The illustrations presented herein are not meant to be actual views of any particular photoimager, but are merely idealized representations that are employed to depict and facilitate description of embodiments of the present invention. Additionally, elements common between figures may retain the same numerical designation.